Birds- Anatomy and Physiology Review

We will take a quick look at common terms related to birds and some unique anatomy and physiology that is important to know if you own birds.

Bones

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• The beak is actually an extension of the jaw bone and is covered with keratin, the same substance that makes up fingernails and hair shafts.

• Certain bones in the bird’s body are called pneumatic bones, which mean that they communicate with the air sacs that are part of a bird’s respiratory system. This allows the birds to be lighter during flight.

• The sternum in birds is called the keel, and is the ridge of bone seen down the center of their chest. Birds with a normal, healthy weight should have a keel that you can feel in sort of a V shape where the chest muscles meet the keel.

Wings and Feathers

• A bird’s wing is uniquely designed for flight. The wrist bones present in mammal skeletons have been fused and simplified, and there are only three true fingers present in a bird’s wing compared to five in mammals’ hands.

• Flight feathers on the wing are termed primary and secondary flight feathers. The primary flight feathers are the long outer 10 feathers starting at the tip of the wing. These allow for thrust as the birds fly, and are equivalent to the engine of a plane. The secondary flight feathers are the remaining feathers toward the body on the wing. These allow for steering as the birds fly, like rudders on a plane or boat. Only the primary flight feathers should be clipped when wing trims are performed. We want to remove the thrust, not the ability to steer!

• Feathers have a direct blood supply when they are first growing. These feathers are called blood feathers, and are easily distinguished from mature feathers by looking at the color of the feather shaft. Blood feathers will have a red or purple shaft, and mature feathers that have lost their blood supply will have a white or clear shaft. Never clip a blood feather because it will bleed and be painful.

Heart, Lungs and Air Sacs

• Birds usually have a well-developed right jugular vein but not a very good left jugular vein. Veterinarians will use this right jugular vein in parrots to obtain blood samples because it is located in a handy featherless tract, which makes the vein easy to see.

• Birds possess a syrinx, which is their voice box and is located at the point where their trachea (windpipe) divides to go to the lungs. This is why birds can make such beautiful sounds and allows some of the parrots the ability to speak. A change in voice can indicate a diseased syrinx.

• Birds have air sacs, which are formed like a bellows system that is connected to the lungs. Gas exchange of oxygen and carbon dioxide occurs in the lungs (just like in us), but then the air is transferred to the air sacs during breathing. It takes two whole breaths for air to move through the entire respiratory system. This gives birds an edge during flight, and is the reason why they can fly very high in low-oxygen altitudes and still not get winded!

• Birds do not have a diaphragm, and breathe by moving their chest to force air in an out of their lungs by using their abdominal muscles. When holding your bird, make sure you do not hold tight enough to restrict this abdominal movement. Doing so can suffocate your bird since they have to physically move to breathe.

Eyes, Ears, Nose and Throat

• Birds can move the muscles in their pupils at will because they are made up of skeletal muscle (like the muscles in your arms or legs). Just as we can flex our biceps consciously, the birds can dilate and constrict their pupils when they get excited or angry. This is called pinning. We humans cannot do this because our pupils are made of smooth muscle, which we do not have conscious control over.

close up of little owl's eye

close up of little owl’s eye

• A bird’s vision is much better than a person’s. Our eyes contain about 200,000 rods and cones, which are the cells that determine visual acuity/sharpness and color. Birds, especially birds of prey such as hawks and owls, can have up to 5 times the number of rods and cones that people have! Birds can also see ultraviolet light, which is outside of our visual spectrum. This is why it is important to offer UV light for your bird if natural sunlight is not available. It is also why birds are brightly colored – the colors are dramatically bright when seen under a UV light, which is the way birds see themselves. This helps attract mates.

• Birds have an opening in the roof of their mouths called a choanal slit, which is a communication between the oral and nasal passages. This is important because occasionally when giving oral medication, if the bird accidentally sucks a little up into the sinuses, you may notice bubbles or some of the medicine come out of the nostrils, or sneezing. This is one reason it is important to give oral medications slowly, a little at a time.

• Birds have a small structure within their nostrils called the operculum. It may resemble a small seed, and some people think that this structure should not be there and should be removed. Leave it is place, though, because this is a normal structure! If you are unsure if there is a foreign body or clog in the nostril, have your avian veterinarian look and see.

Digestive, Reproductive, and Urinary Systems

• Most birds have a crop, which is an out-pocketing of the esophagus located on the right side of the neck. Birds use this crop to store food that they have eaten while foraging. Storing food within their crops allows wild birds to spend less time on the ground (which can be a dangerous place filled with predators). They then fly up to the trees to digest the food as it moves through their digestive tracts. In baby birds that are being hand fed, or in birds with feather loss around their necks, you can see the crop fill up after eating.

• Birds have a gizzard, which is a grinding organ in their digestive tracts. It is important to break down seed hulls, bark, and other hard substances the birds would eat in the wild.

• Birds have separate internal digestive tracts, reproductive tracts, and urinary systems, but they all empty into a common outlet called the cloaca. This is why the droppings have three separate components: the fecal portion, which should be a formed tubular structure (this may change colors depending on the food items eaten so don’t be surprised if it is bright red after your bird gets a pomegranate!), the urine portion (clear liquid portion), and the urates, which are white.

• Both male and female birds have internally located reproductive organs. This makes sexing difficult in species that do not have outward physical differences to tell the sexes apart. Most birds have to be DNA sexed through blood or feather analysis to know for sure whether that bird is male or female.